Device for frequency division



United States Patent DEVICE FOR FREQUENCY DIVISION Nils Tangen, Stockholm, Sweden, assignor to Telefonaktiebolaget L M Ericsson, Stockholm, Sweden, a corporation of Sweden 9 Application December 2, 1953, Serial No. 395,726

Claims priority, application Sweden December 19, 1952 3 Claims. (Cl. 250-36) The present invention relates to a frequency divider comprising an electron tube with a cathode, a control grid and an anode, and at least one further grid, an oscillating circuit with a low Q-value being connected between the control grid and the cathode and in series with the source of voltage, the frequency of which is to be divided, said oscillating circuit being approximately tuned to the desired frequency, and arranged to be fed through a feed-back path from the further grid and the cathode, all the electrodes being series connected with large resistances. The Q-value is the inverted value of the ratio of resistance to reactance for an inductor and may be expressed by the equation:

A device according to the invention is characterized by the input circuit of the electron tube being arranged to be controlled by a relay which, should the voltagefed to the electron tube from the source of voltage fall below a determined value, short circuits by means of its contacts the series connection of part of the resistance connected to the control grid, the oscillating circuit and the input circuit of the electron tube.

The object of the invention is to make the blocking of an electron tube working as an oscillator possible when a voltage connected to said valve and acting as a control voltage deviates a determined minimal magnitude with regard to the amplitude or the frequency without any sudden changes arising, which could cause disturbances of different kinds in for example large carrier frequency systems. With a device according to the invention the impedance between the control grid and the cathode remaining after the relay has become deenergized is still so high, that a change in the direct currents of the electron tube is hardly noticeable. Such change would be definitely noticeable if the relay would short circuit the whole resistance connected to the control grid instead of short circuiting only part of said re sistance while simultaneously a certain capacitive shunting of the gap between the control grid and the cathode is caused, which is unfavourable at high frequencies. The part of the connected resistance comprised in the series connection is chosen so, that the input impedance of the electron valve is approximately constant and independent of whether the relay is actuated or not.

The invention will be described more closely with reference to the accompanying drawing, in which is shown a pentode 1 with a cathode, a control grid 11, 12, a screen grid 13, a suppressor grid 14 and an anode 15. The cathode 11 is connected to a terminal 18 over a cathode resistance 16 and a condenser 17 connected in parallel with said resistance. The control grid 12 is con' nected to a terminal 19 over a resistance 20 and an oscillating circuit 2124. The terminals 18 and 19 represent the input circuit of the electron valve 1. The oscillating circuit 2124 comprises a condenser 24 and a coil 21 connected with said condenser, said coil constituting one of the windings of a transformer 2, the other winding of which is indicated by 22 on the drawing. In parallel with the winding 22 there is an adjust-I able resistance 23, one of the terminals of which is con-' nected to the screen grid 13, and the other terminal of which is series connected to the terminal 18 through 25. An anode battery 27, the positive pole of which" is connected to the anode 15 over a resistance 28, is connected in parallel with the condenser 26, the anode 15 in its turn being connected to one of the output terminals 30 of the device over a condenser 29. The other output terminal 31 of the device is connected to the negative pole of the anode battery 27. The suppressor grid 14 is directly connected to the cathode 11. A rectifier bridge 208 with four rectifying elements is connected between the terminals 18 and 19 and is arranged to feed the coil of a relay 207, which has two break contacts, 203 and 204. The stationary element of the break con tact 203 is connected to the terminal 18 and its movable elements to a tap on the resistance 20. Said last mentioned tap is suitably chosen so that the two parts 201 and 202 of the resistance are approximately equal, that is the part between the oscillating circuit 21-24 and the terminal comprises about half the resistance 20. The break contact 204 is comprised in a series circuit further comprising a battery 206 and an alarm device 205. A crystal oscillator K0 is connected over a filter F to the input circuit of the electron valve 1.

The oscillating circuit 21-24 is presumed to be tuned approximately to the desired frequency. The circuit must have a large L/C-relation, L being the inductance of the winding 21 and C the capacitance of the condenser 24, and a small Q-value. If the crystal controlled oscillator KO emits a sinusoidal negative voltage with the frequency in and a frequency fo/n is desired, n being an integer, the oscillating circuit must be tuned approximately to fo/n.

When the crystal oscillator KO emits a voltage with a suitable frequency and amplitude, it controls the tube 1 working as an oscillator, said tube in its output circuit giving a voltage with such a frequency, as is a sub multiple of the frequency of the crystal oscillator. The coil of the relay 207 is thereby energized and the contacts 203 and 204 are broken.

If the amplitude of the voltage from the crystal 0scillator KO decreases below a determined minimal value, the relay 207 becomes deenergized, the contact 203 thereby short-circuiting the series connection of part of the resistance 20 connected to the control grid, the oscillat ing circuit 2124 and the input circuit 18-19 of the electron tube 1, and the contact 204 connects the alarm device 205 to the battery 206.

If the frequency of the voltage from the crystal oscillator K0 is changed with a determined minimal magni tude from the intended value, such a strong attenuation takes place in the filter F, that the relay 207 becomes deenergized and thereby renders the oscillator tube 1 in operation as previously explained.

I claim:

1. A frequency divider system for dividing the frequency of a source of voltage comprising, in combina tion, electron tube means including a cathode, a control grid, an anode and at least one additional grid, input circuit means for said tube means, oscillating circuit means connected between said control grid and said cathode and including in series the source of voltage the frequency of which is divided, said oscillating circuit means having a low Q-value and being approximately tuned to the desired frequency, feed-back circuit means Patented Mar. 5, 19571 connected to feed said oscillating circuit means from said 7 additional grid and said cathode, a plurality of resistance means of high resistance value, each of the electrodes of the two means being connected to a respective one oi said resistance means, and relay means connected with said input circuit means for control thereby, said relay means controlling contacts connected in series with part of the resistance means connected to the control grid, the oscillating circuit means and the input circuit means, said relay means being set to close its contacts in response to a drop of the voltage fed to the two means from said source of voltage below a predetermined value thereby short circuiting said series circuit including the part of the resistance means.

2. A frequency divider system according to claim 1, wherein said part of the resistance means connected to the control grid constitutes about one half of the total resistance value of said resistance means.

3. A frequency divider system according to claim 1 and further comprising filter means having a narrow pass band included in the circuit connections between said source of voltage and said tube means.

References Cited in the file of this patent UNITED STATES PATENTS Hugenholtz Sept. 11, I951 Hansen et al. Dec. 30, 1952 

